A planar image to be measured is not always uniform. Therefore, it is sometimes necessary to measure the image part by part. This requirement may be satisfied by the provision of a device that uses a conventional streak tube as shown in FIG. 7.
Light from an object 1 is applied through an optical system 202 to a slit 203 so that an image is formed thereon. As a result, the part of the image defined by the slit is obtained. The slit-shaped image part is applied through a relay lens 204 to a conventional streak tube 200.
The slit-shaped optical image is subjected to photoelectric conversion by a photocathode 211, accelerated by a mesh electrode 212, focused by focusing electrodes 213, passed through an aperture 214, and applied to a fluorescent surface 216 through deflecting electrodes 215.
When the linear electron image passes through the deflecting electrodes 215, a ramp voltage is applied across the deflecting electrodes 215. The slit-shaped electron image is streaked by the electric field formed by the ramp voltage to obtain a streak image on the fluorescent surface 216. The streak image is recorded through a lens 207 by a television camera 208.
After the streak image has been taken by the television camera, the slit 203 is vertically moved to the next position by a slit moving means 205, and the above-described series of operations is carried out again. By performing the above-described series of operations in synchronization with the light emission of the object, streak images of the original image can be obtained one after another.
In the above-described device shown in FIG. 7, the mechanical slit is moved to obtain a part of the original image; in other words, whenever it is required to obtain a different part of the original image, it is necessary to move the slit. Therefore, it takes a relatively long period of time to obtain all of the streak images.